Methods and apparatus of video coding using improved matrix-based intra prediction coding mode

ABSTRACT

An electronic apparatus performs a method of updating a most probable modes candidate list for a current block of video data. The electronic apparatus first identifies a neighboring block located at a predefined location relative to the current block and its associated matrix-based intra prediction mode. Next, the electronic apparatus determines a regular intra prediction mode corresponding to the matrix-based intra prediction mode for the neighboring block according to a predefined mathematical relationship between regular intra prediction modes and matrix-based intra prediction modes. Finally, the electronic apparatus inserts the regular intra prediction mode associated with the neighboring block into the most probable modes candidate list according to a predefined order. If the regular intra prediction mode is signaled in the syntax of a video bitstream including the current block, a video decoder will predict the current block from the reconstructed neighboring block according to the regular intra prediction mode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of PCT application No.PCT/US2020/027467, entitled “METHODS AND APPARATUS OF VIDEO CODING USINGIMPROVED MATRIX-BASED INTRA PREDICTION CODING MODE” filed on Apr. 9,2020, which claims the benefit of U.S. Provisional Application No.62/832,203, entitled “MATRIX BASED INTRA PREDICTION CODING MODE FORVIDEO CODING” filed on Apr. 10, 2019, the entire disclosure of both ofwhich is incorporated herein by reference.

TECHNICAL FIELD

The present application generally relates to video data encoding anddecoding, and in particular, to method and system of video coding usingmatrix based intra prediction (MBIP) coding mode.

BACKGROUND

Digital video is supported by a variety of electronic devices, such asdigital televisions, laptop or desktop computers, tablet computers,digital cameras, digital recording devices, digital media players, videogaming consoles, smart phones, video teleconferencing devices, videostreaming devices, etc. The electronic devices transmit, receive,encode, decode, and/or store digital video data by implementing videocompression/decompression standards as defined by MPEG-4, ITU-T H.263,ITU-T H.264/MPEG-4, Part 10, Advanced Video Coding (AVC), HighEfficiency Video Coding (HEVC), and Versatile Video Coding (VVC)standard. Video compression typically includes performing spatial (intraframe) prediction and/or temporal (inter frame) prediction to reduce orremove redundancy inherent in the video data. For block-based videocoding, a video frame is partitioned into one or more slices, each slicehaving multiple video blocks, which may also be referred to as codingtree units (CTUs). Each CTU may contain one coding unit (CU) orrecursively split into smaller CUs until the predefined minimum CU sizeis reached. Each CU (also named leaf CU) contains one or multipletransform units (TUs) and each CU also contains one or multipleprediction units (PUs). Each CU can be coded in either intra, inter orIBC modes. Video blocks in an intra coded (I) slice of a video frame areencoded using spatial prediction with respect to reference samples inneighboring blocks within the same video frame. Video blocks in an intercoded (P or B) slice of a video frame may use spatial prediction withrespect to reference samples in neighboring blocks within the same videoframe or temporal prediction with respect to reference samples in otherprevious and/or future reference video frames.

Spatial or temporal prediction based on a reference block that has beenpreviously encoded, e.g., a neighboring block, results in a predictiveblock for a current video block to be coded. The process of finding thereference block may be accomplished by block matching algorithm.Residual data representing pixel differences between the current blockto be coded and the predictive block is referred to as a residual blockor prediction errors. An inter-coded block is encoded according to amotion vector that points to a reference block in a reference frameforming the predictive block, and the residual block. The process ofdetermining the motion vector is typically referred to as motionestimation. An intra coded block is encoded according to an intraprediction mode and the residual block. For further compression, theresidual block is transformed from the pixel domain to a transformdomain, e.g., frequency domain, resulting in residual transformcoefficients, which may then be quantized. The quantized transformcoefficients, initially arranged in a two-dimensional array, may bescanned to produce a one-dimensional vector of transform coefficients,and then entropy encoded into a video bitstream to achieve even morecompression.

The encoded video bitstream is then saved in a computer-readable storagemedium (e.g., flash memory) to be accessed by another electronic devicewith digital video capability or directly transmitted to the electronicdevice wired or wirelessly. The electronic device then performs videodecompression (which is an opposite process to the video compressiondescribed above) by, e.g., parsing the encoded video bitstream to obtainsyntax elements from the bitstream and reconstructing the digital videodata to its original format from the encoded video bitstream based atleast in part on the syntax elements obtained from the bitstream, andrenders the reconstructed digital video data on a display of theelectronic device.

With digital video quality going from high definition, to 4K×2K or even8K×4K, the amount of video data to be encoded/decoded growsexponentially. It is a constant challenge in terms of how the video datacan be encoded/decoded more efficiently while maintaining the imagequality of the decoded video data.

For example, the conventional intra prediction mode performs angularprediction to a current coding block by referencing the reconstructedpixels from neighboring blocks through direct copying or interpolation.As a result, the predicted samples using the conventional intraprediction mode have limited freedom of pixel value variation,especially along the prediction direction. To further improve the codingefficiency, matrix based intra prediction (MBIP) mode is introduced byapplying linear matrix transformation on reconstructed pixels in theneighboring blocks to predict samples of the current coding block. Butthe current implementation of MBIP presents new challenges to thehardware/software implementations, e.g., requiring complicated look-uptable operations between coding blocks using different types of intraprediction methods and occupying a significant amount of space(especially on-chip) for storing the matrix coefficients.

SUMMARY

The present application describes implementations related to video dataencoding and decoding and, more particularly, to system and method ofvideo encoding and decoding using improved matrix based intra prediction(MBIP) coding mode.

According to a first aspect of the present application, a method ofupdating a most probable modes candidate list for a current block ofvideo data is performed at an electronic apparatus having one or moreprocessing units and memory storing a plurality of programs to beexecuted by the one or more processing units. The method includes:identifying a neighboring block located at a predefined locationrelative to the current block and its associated matrix-based intraprediction mode; determining a regular intra prediction modecorresponding to the matrix-based intra prediction mode for theneighboring block according to a predefined mathematical relationshipbetween regular intra prediction modes and matrix-based intra predictionmodes; and inserting the regular intra prediction mode associated withthe neighboring block into the most probable modes candidate listaccording to a predefined order.

According to a second aspect of the present application, an electronicapparatus includes one or more processing units, memory and a pluralityof programs stored in the memory. The programs, when executed by the oneor more processing units, cause the electronic apparatus to perform themethod of updating a most probable modes candidate list for a currentblock of video data as described above.

According to a third aspect of the present application, a non-transitorycomputer readable storage medium stores a plurality of programs forexecution by an electronic apparatus having one or more processingunits. The programs, when executed by the one or more processing units,cause the electronic apparatus to perform the method of updating a mostprobable modes candidate list for a current block of video data asdescribed above.

According to a fourth aspect of the present application, a method ofpredicting a current block of video data using matrix-based intraprediction is performed at an electronic apparatus having one or moreprocessing units and memory storing a plurality of programs to beexecuted by the one or more processing units. The method includes:identifying one or more neighboring blocks relative to the currentblock; selecting, among a plurality of matrix-based intra predictionmodes, a matrix-based intra prediction mode for predicting the currentblock; retrieving, from a storage device, coefficients of a matrix and abias vector corresponding to the selected matrix-based intra predictionmode; and performing matrix-based intra prediction to the identified oneor more neighboring blocks using the retrieved coefficients of thematrix and the bias vector.

According to a fifth aspect of the present application, an electronicapparatus includes one or more processing units, memory and a pluralityof programs stored in the memory. The programs, when executed by the oneor more processing units, cause the electronic apparatus to perform themethod of predicting a current block of video data using matrix-basedintra prediction as described above.

According to a sixth aspect of the present application, a non-transitorycomputer readable storage medium stores a plurality of programs forexecution by an electronic apparatus having one or more processingunits. The programs, when executed by the one or more processing units,cause the electronic apparatus to perform the method of predicting acurrent block of video data using matrix-based intra prediction asdescribed above.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the implementations and are incorporated herein andconstitute a part of the specification, illustrate the describedimplementations and together with the description serve to explain theunderlying principles. Like reference numerals refer to correspondingparts.

FIG. 1 is a block diagram illustrating an exemplary video encoding anddecoding system in accordance with some implementations of the presentdisclosure.

FIG. 2 is a block diagram illustrating an exemplary video encoder inaccordance with some implementations of the present disclosure.

FIG. 3 is a block diagram illustrating an exemplary video decoder inaccordance with some implementations of the present disclosure.

FIGS. 4A-4D are block diagrams illustrating how a frame is recursivelyquad-tree partitioned into multiple video blocks of different sizes inaccordance with some implementations of the present disclosure.

FIG. 5A is a block diagram illustrating 67 candidate intra predictionmodes for predicting a current coding block based on the reconstructedneighboring blocks in accordance with some implementations of thepresent disclosure.

FIG. 5B is a block diagram illustrating exemplary locations of fivereconstructed neighboring blocks of a current coding block in accordancewith some implementations of the present disclosure.

FIGS. 6A and 6B are block diagrams illustrating two matrix-based intraprediction schemes of coding blocks of different sizes in accordancewith some implementations of the present disclosure.

FIG. 7 is a flowchart illustrating an exemplary process by which a videocoder implements the techniques of generating a most probable modes(MPM) candidate list in accordance with some implementations of thepresent disclosure.

DETAILED DESCRIPTION

Reference will now be made in detail to specific implementations,examples of which are illustrated in the accompanying drawings. In thefollowing detailed description, numerous non-limiting specific detailsare set forth in order to assist in understanding the subject matterpresented herein. But it will be apparent to one of ordinary skill inthe art that various alternatives may be used without departing from thescope of claims and the subject matter may be practiced without thesespecific details. For example, it will be apparent to one of ordinaryskill in the art that the subject matter presented herein can beimplemented on many types of electronic devices with digital videocapabilities.

FIG. 1 is a block diagram illustrating an exemplary system 10 forencoding and decoding video blocks in parallel in accordance with someimplementations of the present disclosure. As shown in FIG. 1, system 10includes a source device 12 that generates and encodes video data to bedecoded at a later time by a destination device 14. Source device 12 anddestination device 14 may comprise any of a wide variety of electronicdevices, including desktop or laptop computers, tablet computers, smartphones, set-top boxes, digital televisions, cameras, display devices,digital media players, video gaming consoles, video streaming device, orthe like. In some implementations, source device 12 and destinationdevice 14 are equipped with wireless communication capabilities.

In some implementations, destination device 14 may receive the encodedvideo data to be decoded via a link 16. Link 16 may comprise any type ofcommunication medium or device capable of moving the encoded video datafrom source device 12 to destination device 14. In one example, link 16may comprise a communication medium to enable source device 12 totransmit the encoded video data directly to destination device 14 inreal-time. The encoded video data may be modulated according to acommunication standard, such as a wireless communication protocol, andtransmitted to destination device 14. The communication medium maycomprise any wireless or wired communication medium, such as a radiofrequency (RF) spectrum or one or more physical transmission lines. Thecommunication medium may form part of a packet-based network, such as alocal area network, a wide-area network, or a global network such as theInternet. The communication medium may include routers, switches, basestations, or any other equipment that may be useful to facilitatecommunication from source device 12 to destination device 14.

In some other implementations, the encoded video data may be transmittedfrom output interface 22 to a storage device 32. Subsequently, theencoded video data in storage device 32 may be accessed by destinationdevice 14 via input interface 28. Storage device 32 may include any of avariety of distributed or locally accessed data storage media such as ahard drive, Blu-ray discs, DVDs, CD-ROMs, flash memory, volatile ornon-volatile memory, or any other suitable digital storage media forstoring encoded video data. In a further example, storage device 32 maycorrespond to a file server or another intermediate storage device thatmay hold the encoded video data generated by source device 12.Destination device 14 may access the stored video data from storagedevice 32 via streaming or downloading. The file server may be any typeof computer capable of storing encoded video data and transmitting theencoded video data to destination device 14. Exemplary file serversinclude a web server (e.g., for a website), an FTP server, networkattached storage (NAS) devices, or a local disk drive. Destinationdevice 14 may access the encoded video data through any standard dataconnection, including a wireless channel (e.g., a Wi-Fi connection), awired connection (e.g., DSL, cable modem, etc.), or a combination ofboth that is suitable for accessing encoded video data stored on a fileserver. The transmission of encoded video data from storage device 32may be a streaming transmission, a download transmission, or acombination of both.

As shown in FIG. 1, source device 12 includes a video source 18, a videoencoder 20 and an output interface 22. Video source 18 may include asource such as a video capture device, e.g., a video camera, a videoarchive containing previously captured video, a video feed interface toreceive video from a video content provider, and/or a computer graphicssystem for generating computer graphics data as the source video, or acombination of such sources. As one example, if video source 18 is avideo camera of a security surveillance system, source device 12 anddestination device 14 may form camera phones or video phones. However,the implementations described in the present application may beapplicable to video coding in general, and may be applied to wirelessand/or wired applications.

The captured, pre-captured, or computer-generated video may be encodedby video encoder 20. The encoded video data may be transmitted directlyto destination device 14 via output interface 22 of source device 12.The encoded video data may also (or alternatively) be stored ontostorage device 32 for later access by destination device 14 or otherdevices, for decoding and/or playback. Output interface 22 may furtherinclude a modem and/or a transmitter.

Destination device 14 includes an input interface 28, a video decoder30, and a display device 34. Input interface 28 may include a receiverand/or a modem and receive the encoded video data over link 16. Theencoded video data communicated over link 16, or provided on storagedevice 32, may include a variety of syntax elements generated by videoencoder 20 for use by video decoder 30 in decoding the video data. Suchsyntax elements may be included within the encoded video datatransmitted on a communication medium, stored on a storage medium, orstored a file server.

In some implementations, destination device 14 may include a displaydevice 34, which can be an integrated display device and an externaldisplay device that is configured to communicate with destination device14. Display device 34 displays the decoded video data to a user, and maycomprise any of a variety of display devices such as a liquid crystaldisplay (LCD), a plasma display, an organic light emitting diode (OLED)display, or another type of display device.

Video encoder 20 and video decoder 30 may operate according toproprietary or industry standards, such as VVC, HEVC, MPEG-4, Part 10,Advanced Video Coding (AVC), or extensions of such standards. It shouldbe understood that the present application is not limited to a specificvideo coding/decoding standard and may be applicable to other videocoding/decoding standards. It is generally contemplated that videoencoder 20 of source device 12 may be configured to encode video dataaccording to any of these current or future standards. Similarly, it isalso generally contemplated that video decoder 30 of destination device14 may be configured to decode video data according to any of thesecurrent or future standards.

Video encoder 20 and video decoder 30 each may be implemented as any ofa variety of suitable encoder circuitry, such as one or moremicroprocessors, digital signal processors (DSPs), application specificintegrated circuits (ASICs), field programmable gate arrays (FPGAs),discrete logic, software, hardware, firmware or any combinationsthereof. When implemented partially in software, an electronic devicemay store instructions for the software in a suitable, non-transitorycomputer-readable medium and execute the instructions in hardware usingone or more processors to perform the video coding/decoding operationsdisclosed in the present disclosure. Each of video encoder 20 and videodecoder 30 may be included in one or more encoders or decoders, eitherof which may be integrated as part of a combined encoder/decoder (CODEC)in a respective device.

FIG. 2 is a block diagram illustrating an exemplary video encoder 20 inaccordance with some implementations described in the presentapplication. Video encoder 20 may perform intra and inter predictivecoding of video blocks within video frames. Intra predictive codingrelies on spatial prediction to reduce or remove spatial redundancy invideo data within a given video frame or picture. Inter predictivecoding relies on temporal prediction to reduce or remove temporalredundancy in video data within adjacent video frames or pictures of avideo sequence.

As shown in FIG. 2, video encoder 20 includes video data memory 40,prediction processing unit 41, decoded picture buffer (DPB) 64, summer50, transform processing unit 52, quantization unit 54, and entropyencoding unit 56. Prediction processing unit 41 further includes motionestimation unit 42, motion compensation unit 44, partition unit 45,intra prediction processing unit 46, and intra block copy (BC) unit 48.In some implementations, video encoder 20 also includes inversequantization unit 58, inverse transform processing unit 60, and summer62 for video block reconstruction. A deblocking filter (not shown) maybe positioned between summer 62 and DPB 64 to filter block boundaries toremove blockiness artifacts from reconstructed video. An in loop filter(not shown) may also be used in addition to the deblocking filter tofilter the output of summer 62. Video encoder 20 may take the form of afixed or programmable hardware unit or may be divided among one or moreof the illustrated fixed or programmable hardware units.

Video data memory 40 may store video data to be encoded by thecomponents of video encoder 20. The video data in video data memory 40may be obtained, for example, from video source 18. DPB 64 is a bufferthat stores reference video data for use in encoding video data by videoencoder 20 (e.g., in intra or inter predictive coding modes). Video datamemory 40 and DPB 64 may be formed by any of a variety of memorydevices. In various examples, video data memory 40 may be on-chip withother components of video encoder 20, or off-chip relative to thosecomponents.

As shown in FIG. 2, after receiving video data, partition unit 45 withinprediction processing unit 41 partitions the video data into videoblocks. This partitioning may also include partitioning a video frameinto slices, tiles, or other larger coding units (CUs) according to apredefined splitting structures such as quad-tree structure associatedwith the video data. The video frame may be divided into multiple videoblocks (or sets of video blocks referred to as tiles). Predictionprocessing unit 41 may select one of a plurality of possible predictivecoding modes, such as one of a plurality of intra predictive codingmodes or one of a plurality of inter predictive coding modes, for thecurrent video block based on error results (e.g., coding rate and thelevel of distortion). Prediction processing unit 41 may provide theresulting intra or inter prediction coded block to summer 50 to generatea residual block and to summer 62 to reconstruct the encoded block foruse as part of a reference frame subsequently. Prediction processingunit 41 also provides syntax elements, such as motion vectors,intra-mode indicators, partition information, and other such syntaxinformation, to entropy encoding unit 56.

In order to select an appropriate intra predictive coding mode for thecurrent video block, intra prediction processing unit 46 withinprediction processing unit 41 may perform intra predictive coding of thecurrent video block relative to one or more neighboring blocks in thesame frame as the current block to be coded to provide spatialprediction. Motion estimation unit 42 and motion compensation unit 44within prediction processing unit 41 perform inter predictive coding ofthe current video block relative to one or more predictive blocks in oneor more reference frames to provide temporal prediction. Video encoder20 may perform multiple coding passes, e.g., to select an appropriatecoding mode for each block of video data.

In some implementations, motion estimation unit 42 determines the interprediction mode for a current video frame by generating a motion vector,which indicates the displacement of a prediction unit (PU) of a videoblock within the current video frame relative to a predictive blockwithin a reference video frame, according to a predetermined patternwithin a sequence of video frames. Motion estimation, performed bymotion estimation unit 42, is the process of generating motion vectors,which estimate motion for video blocks. A motion vector, for example,may indicate the displacement of a PU of a video block within a currentvideo frame or picture relative to a predictive block within a referenceframe (or other coded unit) relative to the current block being codedwithin the current frame (or other coded unit). The predeterminedpattern may designate video frames in the sequence as P frames or Bframes. Intra BC unit 48 may determine vectors, e.g., block vectors, forintra BC coding in a manner similar to the determination of motionvectors by motion estimation unit 42 for inter prediction, or mayutilize motion estimation unit 42 to determine the block vector.

A predictive block is a block of a reference frame that is deemed asclosely matching the PU of the video block to be coded in terms of pixeldifference, which may be determined by sum of absolute difference (SAD),sum of square difference (SSD), or other difference metrics. In someimplementations, video encoder 20 may calculate values for sub-integerpixel positions of reference frames stored in DPB 64. For example, videoencoder 20 may interpolate values of one-quarter pixel positions,one-eighth pixel positions, or other fractional pixel positions of thereference frame. Therefore, motion estimation unit 42 may perform amotion search relative to the full pixel positions and fractional pixelpositions and output a motion vector with fractional pixel precision.

Motion estimation unit 42 calculates a motion vector for a PU of a videoblock in an inter prediction coded frame by comparing the position ofthe PU to the position of a predictive block of a reference frameselected from a first reference frame list (List 0) or a secondreference frame list (List 1), each of which identifies one or morereference frames stored in DPB 64. Motion estimation unit 42 sends thecalculated motion vector to motion compensation unit 44 and then toentropy encoding unit 56.

Motion compensation, performed by motion compensation unit 44, mayinvolve fetching or generating the predictive block based on the motionvector determined by motion estimation unit 42. Upon receiving themotion vector for the PU of the current video block, motion compensationunit 44 may locate a predictive block to which the motion vector pointsin one of the reference frame lists, retrieve the predictive block fromDPB 64, and forward the predictive block to summer 50. Summer 50 thenforms a residual video block of pixel difference values by subtractingpixel values of the predictive block provided by motion compensationunit 44 from the pixel values of the current video block being coded.The pixel difference values forming the residual video block may includeluma or chroma difference components or both. Motion compensation unit44 may also generate syntax elements associated with the video blocks ofa video frame for use by video decoder 30 in decoding the video blocksof the video frame. The syntax elements may include, for example, syntaxelements defining the motion vector used to identify the predictiveblock, any flags indicating the prediction mode, or any other syntaxinformation described herein. Note that motion estimation unit 42 andmotion compensation unit 44 may be highly integrated, but areillustrated separately for conceptual purposes.

In some implementations, intra BC unit 48 may generate vectors and fetchpredictive blocks in a manner similar to that described above inconnection with motion estimation unit 42 and motion compensation unit44, but with the predictive blocks being in the same frame as thecurrent block being coded and with the vectors being referred to asblock vectors as opposed to motion vectors. In particular, intra BC unit48 may determine an intra-prediction mode to use to encode a currentblock. In some examples, intra BC unit 48 may encode a current blockusing various intra-prediction modes, e.g., during separate encodingpasses, and test their performance through rate-distortion analysis.Next, intra BC unit 48 may select, among the various testedintra-prediction modes, an appropriate intra-prediction mode to use andgenerate an intra-mode indicator accordingly. For example, intra BC unit48 may calculate rate-distortion values using a rate-distortion analysisfor the various tested intra-prediction modes, and select theintra-prediction mode having the best rate-distortion characteristicsamong the tested modes as the appropriate intra-prediction mode to use.Rate-distortion analysis generally determines an amount of distortion(or error) between an encoded block and an original, unencoded blockthat was encoded to produce the encoded block, as well as a bitrate(i.e., a number of bits) used to produce the encoded block. Intra BCunit 48 may calculate ratios from the distortions and rates for thevarious encoded blocks to determine which intra-prediction mode exhibitsthe best rate-distortion value for the block.

In other examples, intra BC unit 48 may use motion estimation unit 42and motion compensation unit 44, in whole or in part, to perform suchfunctions for Intra BC prediction according to the implementationsdescribed herein. In either case, for Intra block copy, a predictiveblock may be a block that is deemed as closely matching the block to becoded, in terms of pixel difference, which may be determined by sum ofabsolute difference (SAD), sum of squared difference (SSD), or otherdifference metrics, and identification of the predictive block mayinclude calculation of values for sub-integer pixel positions.

Whether the predictive block is from the same frame according to intraprediction, or a different frame according to inter prediction, videoencoder 20 may form a residual video block by subtracting pixel valuesof the predictive block from the pixel values of the current video blockbeing coded, forming pixel difference values. The pixel differencevalues forming the residual video block may include both luma and chromacomponent differences.

Intra prediction processing unit 46 may intra-predict a current videoblock, as an alternative to the inter-prediction performed by motionestimation unit 42 and motion compensation unit 44, or the intra blockcopy prediction performed by intra BC unit 48, as described above. Inparticular, intra prediction processing unit 46 may determine an intraprediction mode to use to encode a current block. To do so, intraprediction processing unit 46 may encode a current block using variousintra prediction modes, e.g., during separate encoding passes, and intraprediction processing unit 46 (or a mode select unit, in some examples)may select an appropriate intra prediction mode to use from the testedintra prediction modes. Intra prediction processing unit 46 may provideinformation indicative of the selected intra-prediction mode for theblock to entropy encoding unit 56. Entropy encoding unit 56 may encodethe information indicating the selected intra-prediction mode in thebitstream.

After prediction processing unit 41 determines the predictive block forthe current video block via either inter prediction or intra prediction,summer 50 forms a residual video block by subtracting the predictiveblock from the current video block. The residual video data in theresidual block may be included in one or more transform units (TUs) andis provided to transform processing unit 52. Transform processing unit52 transforms the residual video data into residual transformcoefficients using a transform, such as a discrete cosine transform(DCT) or a conceptually similar transform.

Transform processing unit 52 may send the resulting transformcoefficients to quantization unit 54. Quantization unit 54 quantizes thetransform coefficients to further reduce bit rate. The quantizationprocess may also reduce the bit depth associated with some or all of thecoefficients. The degree of quantization may be modified by adjusting aquantization parameter. In some examples, quantization unit 54 may thenperform a scan of a matrix including the quantized transformcoefficients. Alternatively, entropy encoding unit 56 may perform thescan.

Following quantization, entropy encoding unit 56 entropy encodes thequantized transform coefficients into a video bitstream using, e.g.,context adaptive variable length coding (CAVLC), context adaptive binaryarithmetic coding (CABAC), syntax-based context-adaptive binaryarithmetic coding (SBAC), probability interval partitioning entropy(PIPE) coding or another entropy encoding methodology or technique. Theencoded bitstream may then be transmitted to video decoder 30, orarchived in storage device 32 for later transmission to or retrieval byvideo decoder 30. Entropy encoding unit 56 may also entropy encode themotion vectors and the other syntax elements for the current video framebeing coded.

Inverse quantization unit 58 and inverse transform processing unit 60apply inverse quantization and inverse transformation, respectively, toreconstruct the residual video block in the pixel domain for generatinga reference block for prediction of other video blocks. As noted above,motion compensation unit 44 may generate a motion compensated predictiveblock from one or more reference blocks of the frames stored in DPB 64.Motion compensation unit 44 may also apply one or more interpolationfilters to the predictive block to calculate sub-integer pixel valuesfor use in motion estimation.

Summer 62 adds the reconstructed residual block to the motioncompensated predictive block produced by motion compensation unit 44 toproduce a reference block for storage in DPB 64. The reference block maythen be used by intra BC unit 48, motion estimation unit 42 and motioncompensation unit 44 as a predictive block to inter predict anothervideo block in a subsequent video frame.

FIG. 3 is a block diagram illustrating an exemplary video decoder 30 inaccordance with some implementations of the present application. Videodecoder 30 includes video data memory 79, entropy decoding unit 80,prediction processing unit 81, inverse quantization unit 86, inversetransform processing unit 88, summer 90, and DPB 92. Predictionprocessing unit 81 further includes motion compensation unit 82, intraprediction unit 84, and intra BC unit 85. Video decoder 30 may perform adecoding process generally reciprocal to the encoding process describedabove with respect to video encoder 20 in connection with FIG. 2. Forexample, motion compensation unit 82 may generate prediction data basedon motion vectors received from entropy decoding unit 80, whileintra-prediction unit 84 may generate prediction data based onintra-prediction mode indicators received from entropy decoding unit 80.

In some examples, a unit of video decoder 30 may be tasked to performthe implementations of the present application. Also, in some examples,the implementations of the present disclosure may be divided among oneor more of the units of video decoder 30. For example, intra BC unit 85may perform the implementations of the present application, alone, or incombination with other units of video decoder 30, such as motioncompensation unit 82, intra prediction unit 84, and entropy decodingunit 80. In some examples, video decoder 30 may not include intra BCunit 85 and the functionality of intra BC unit 85 may be performed byother components of prediction processing unit 81, such as motioncompensation unit 82.

Video data memory 79 may store video data, such as an encoded videobitstream, to be decoded by the other components of video decoder 30.The video data stored in video data memory 79 may be obtained, forexample, from storage device 32, from a local video source, such as acamera, via wired or wireless network communication of video data, or byaccessing physical data storage media (e.g., a flash drive or harddisk). Video data memory 79 may include a coded picture buffer (CPB)that stores encoded video data from an encoded video bitstream. Decodedpicture buffer (DPB) 92 of video decoder 30 stores reference video datafor use in decoding video data by video decoder 30 (e.g., in intra orinter predictive coding modes). Video data memory 79 and DPB 92 may beformed by any of a variety of memory devices, such as dynamic randomaccess memory (DRAM), including synchronous DRAM (SDRAM),magneto-resistive RAM (MRAM), resistive RAM (RRAM), or other types ofmemory devices. For illustrative purpose, video data memory 79 and DPB92 are depicted as two distinct components of video decoder 30 in FIG.3. But it will be apparent to one skilled in the art that video datamemory 79 and DPB 92 may be provided by the same memory device orseparate memory devices. In some examples, video data memory 79 may beon-chip with other components of video decoder 30, or off-chip relativeto those components.

During the decoding process, video decoder 30 receives an encoded videobitstream that represents video blocks of an encoded video frame andassociated syntax elements. Video decoder 30 may receive the syntaxelements at the video frame level and/or the video block level. Entropydecoding unit 80 of video decoder 30 entropy decodes the bitstream togenerate quantized coefficients, motion vectors or intra-prediction modeindicators, and other syntax elements. Entropy decoding unit 80 thenforwards the motion vectors and other syntax elements to predictionprocessing unit 81.

When the video frame is coded as an intra predictive coded (I) frame orfor intra coded predictive blocks in other types of frames, intraprediction unit 84 of prediction processing unit 81 may generateprediction data for a video block of the current video frame based on asignaled intra prediction mode and reference data from previouslydecoded blocks of the current frame.

When the video frame is coded as an inter-predictive coded (i.e., B orP) frame, motion compensation unit 82 of prediction processing unit 81produces one or more predictive blocks for a video block of the currentvideo frame based on the motion vectors and other syntax elementsreceived from entropy decoding unit 80. Each of the predictive blocksmay be produced from a reference frame within one of the reference framelists. Video decoder 30 may construct the reference frame lists, List 0and List 1, using default construction techniques based on referenceframes stored in DPB 92.

In some examples, when the video block is coded according to the intraBC mode described herein, intra BC unit 85 of prediction processing unit81 produces predictive blocks for the current video block based on blockvectors and other syntax elements received from entropy decoding unit80. The predictive blocks may be within a reconstructed region of thesame picture as the current video block defined by video encoder 20.

Motion compensation unit 82 and/or intra BC unit 85 determinesprediction information for a video block of the current video frame byparsing the motion vectors and other syntax elements, and then uses theprediction information to produce the predictive blocks for the currentvideo block being decoded. For example, motion compensation unit 82 usessome of the received syntax elements to determine a prediction mode(e.g., intra or inter prediction) used to code video blocks of the videoframe, an inter prediction frame type (e.g., B or P), constructioninformation for one or more of the reference frame lists for the frame,motion vectors for each inter predictive encoded video block of theframe, inter prediction status for each inter predictive coded videoblock of the frame, and other information to decode the video blocks inthe current video frame.

Similarly, intra BC unit 85 may use some of the received syntaxelements, e.g., a flag, to determine that the current video block waspredicted using the intra BC mode, construction information of whichvideo blocks of the frame are within the reconstructed region and shouldbe stored in DPB 92, block vectors for each intra BC predicted videoblock of the frame, intra BC prediction status for each intra BCpredicted video block of the frame, and other information to decode thevideo blocks in the current video frame.

Motion compensation unit 82 may also perform interpolation using theinterpolation filters as used by video encoder 20 during encoding of thevideo blocks to calculate interpolated values for sub-integer pixels ofreference blocks. In this case, motion compensation unit 82 maydetermine the interpolation filters used by video encoder 20 from thereceived syntax elements and use the interpolation filters to producepredictive blocks.

Inverse quantization unit 86 inverse quantizes the quantized transformcoefficients provided in the bitstream and entropy decoded by entropydecoding unit 80 using the same quantization parameter calculated byvideo encoder 20 for each video block in the video frame to determine adegree of quantization. Inverse transform processing unit 88 applies aninverse transform, e.g., an inverse DCT, an inverse integer transform,or a conceptually similar inverse transform process, to the transformcoefficients in order to reconstruct the residual blocks in the pixeldomain.

After motion compensation unit 82 or intra BC unit 85 generates thepredictive block for the current video block based on the vectors andother syntax elements, summer 90 reconstructs decoded video block forthe current video block by summing the residual block from inversetransform processing unit 88 and a corresponding predictive blockgenerated by motion compensation unit 82 and intra BC unit 85. Anin-loop filter (not pictured) may be positioned between summer 90 andDPB 92 to further process the decoded video block. The decoded videoblocks in a given frame are then stored in DPB 92, which storesreference frames used for subsequent motion compensation of next videoblocks. DPB 92, or a memory device separate from DPB 92, may also storedecoded video for later presentation on a display device, such asdisplay device 34 of FIG. 1.

In a typical video coding process, a video sequence typically includesan ordered set of frames or pictures. Each frame may include threesample arrays, denoted SL, SCb, and SCr. SL is a two-dimensional arrayof luma samples. SCb is a two-dimensional array of Cb chroma samples.SCr is a two-dimensional array of Cr chroma samples. In other instances,a frame may be monochrome and therefore includes only onetwo-dimensional array of luma samples.

As shown in FIG. 4A, video encoder 20 (or more specifically partitionunit 45) generates an encoded representation of a frame by firstpartitioning the frame into a set of coding tree units (CTUs). A videoframe may include an integer number of CTUs ordered consecutively in araster scan order from left to right and from top to bottom. Each CTU isa largest logical coding unit and the width and height of the CTU aresignaled by the video encoder 20 in a sequence parameter set, such thatall the CTUs in a video sequence have the same size being one of128×128, 64×64, 32×32, and 16×16. But it should be noted that thepresent application is not necessarily limited to a particular size. Asshown in FIG. 4B, each CTU may comprise one coding tree block (CTB) ofluma samples, two corresponding coding tree blocks of chroma samples,and syntax elements used to code the samples of the coding tree blocks.The syntax elements describe properties of different types of units of acoded block of pixels and how the video sequence can be reconstructed atthe video decoder 30, including inter or intra prediction, intraprediction mode, motion vectors, and other parameters. In monochromepictures or pictures having three separate color planes, a CTU maycomprise a single coding tree block and syntax elements used to code thesamples of the coding tree block. A coding tree block may be an N×Nblock of samples.

To achieve a better performance, video encoder 20 may recursivelyperform tree partitioning such as binary-tree partitioning, quad-treepartitioning or a combination of both on the coding tree blocks of theCTU and divide the CTU into smaller coding units (CUs). As depicted inFIG. 4C, the 64×64 CTU 400 is first divided into four smaller CU, eachhaving a block size of 32×32. Among the four smaller CUs, CU 410 and CU420 are each divided into four CUs of 16×16 by block size. The two 16×16CUs 430 and 440 are each further divided into four CUs of 8×8 by blocksize. FIG. 4D depicts a quad-tree data structure illustrating the endresult of the partition process of the CTU 400 as depicted in FIG. 4C,each leaf node of the quad-tree corresponding to one CU of a respectivesize ranging from 32×32 to 8×8. Like the CTU depicted in FIG. 4B, eachCU may comprise a coding block (CB) of luma samples and twocorresponding coding blocks of chroma samples of a frame of the samesize, and syntax elements used to code the samples of the coding blocks.In monochrome pictures or pictures having three separate color planes, aCU may comprise a single coding block and syntax structures used to codethe samples of the coding block.

In some implementations, video encoder 20 may further partition a codingblock of a CU into one or more M×N prediction blocks (PB). A predictionblock is a rectangular (square or non-square) block of samples on whichthe same prediction, inter or intra, is applied. A prediction unit (PU)of a CU may comprise a prediction block of luma samples, twocorresponding prediction blocks of chroma samples, and syntax elementsused to predict the prediction blocks. In monochrome pictures orpictures having three separate color planes, a PU may comprise a singleprediction block and syntax structures used to predict the predictionblock. Video encoder 20 may generate predictive luma, Cb, and Cr blocksfor luma, Cb, and Cr prediction blocks of each PU of the CU.

Video encoder 20 may use intra prediction or inter prediction togenerate the predictive blocks for a PU. If video encoder 20 uses intraprediction to generate the predictive blocks of a PU, video encoder 20may generate the predictive blocks of the PU based on decoded samples ofthe frame associated with the PU. If video encoder 20 uses interprediction to generate the predictive blocks of a PU, video encoder 20may generate the predictive blocks of the PU based on decoded samples ofone or more frames other than the frame associated with the PU.

After video encoder 20 generates predictive luma, Cb, and Cr blocks forone or more PUs of a CU, video encoder 20 may generate a luma residualblock for the CU by subtracting the CU's predictive luma blocks from itsoriginal luma coding block such that each sample in the CU's lumaresidual block indicates a difference between a luma sample in one ofthe CU's predictive luma blocks and a corresponding sample in the CU'soriginal luma coding block. Similarly, video encoder 20 may generate aCb residual block and a Cr residual block for the CU, respectively, suchthat each sample in the CU's Cb residual block indicates a differencebetween a Cb sample in one of the CU's predictive Cb blocks and acorresponding sample in the CU's original Cb coding block and eachsample in the CU's Cr residual block may indicate a difference between aCr sample in one of the CU's predictive Cr blocks and a correspondingsample in the CU's original Cr coding block.

Furthermore, as illustrated in FIG. 4C, video encoder 20 may usequad-tree partitioning to decompose the luma, Cb, and Cr residual blocksof a CU into one or more luma, Cb, and Cr transform blocks. A transformblock is a rectangular (square or non-square) block of samples on whichthe same transform is applied. A transform unit (TU) of a CU maycomprise a transform block of luma samples, two corresponding transformblocks of chroma samples, and syntax elements used to transform thetransform block samples. Thus, each TU of a CU may be associated with aluma transform block, a Cb transform block, and a Cr transform block. Insome examples, the luma transform block associated with the TU may be asub-block of the CU's luma residual block. The Cb transform block may bea sub-block of the CU's Cb residual block. The Cr transform block may bea sub-block of the CU's Cr residual block. In monochrome pictures orpictures having three separate color planes, a TU may comprise a singletransform block and syntax structures used to transform the samples ofthe transform block.

Video encoder 20 may apply one or more transforms to a luma transformblock of a TU to generate a luma coefficient block for the TU. Acoefficient block may be a two-dimensional array of transformcoefficients. A transform coefficient may be a scalar quantity. Videoencoder 20 may apply one or more transforms to a Cb transform block of aTU to generate a Cb coefficient block for the TU. Video encoder 20 mayapply one or more transforms to a Cr transform block of a TU to generatea Cr coefficient block for the TU.

After generating a coefficient block (e.g., a luma coefficient block, aCb coefficient block or a Cr coefficient block), video encoder 20 mayquantize the coefficient block. Quantization generally refers to aprocess in which transform coefficients are quantized to possibly reducethe amount of data used to represent the transform coefficients,providing further compression. After video encoder 20 quantizes acoefficient block, video encoder 20 may entropy encode syntax elementsindicating the quantized transform coefficients. For example, videoencoder 20 may perform Context-Adaptive Binary Arithmetic Coding (CABAC)on the syntax elements indicating the quantized transform coefficients.Finally, video encoder 20 may output a bitstream that includes asequence of bits that forms a representation of coded frames andassociated data, which is either saved in storage device 32 ortransmitted to destination device 14.

After receiving a bitstream generated by video encoder 20, video decoder30 may parse the bitstream to obtain syntax elements from the bitstream.Video decoder 30 may reconstruct the frames of the video data based atleast in part on the syntax elements obtained from the bitstream. Theprocess of reconstructing the video data is generally reciprocal to theencoding process performed by video encoder 20. For example, videodecoder 30 may perform inverse transforms on the coefficient blocksassociated with TUs of a current CU to reconstruct residual blocksassociated with the TUs of the current CU. Video decoder 30 alsoreconstructs the coding blocks of the current CU by adding the samplesof the predictive blocks for PUs of the current CU to correspondingsamples of the transform blocks of the TUs of the current CU. Afterreconstructing the coding blocks for each CU of a frame, video decoder30 may reconstruct the frame.

As noted above, video coding achieves video compression using primarilytwo modes, i.e., intra-frame prediction (or intra-prediction) andinter-frame prediction (or inter-prediction). It is noted that IBC couldbe regarded as either intra-frame prediction or a third mode. Betweenthe two modes, inter-frame prediction contributes more to the codingefficiency than intra-frame prediction because of the use of motionvectors for predicting a current video block from a reference videoblock.

FIG. 5A is a block diagram illustrating 67 regular intra predictionmodes for predicting a current coding block based on the reconstructedneighboring blocks in accordance with some implementations of thepresent disclosure. The 67 regular intra prediction modes includes 65angular modes (shown with mode indexes 2 to 33 being the “horizontalmodes set” and mode indexes 34-66 being the “vertical modes set”) plustwo non-angular modes, referred to as the “planar mode” (mode index 0)and the “DC mode” (mode index 1), which are collectively referred to as“non-angular modes set”. The implementations of this disclosure isapplied for any number of angular modes used for intra prediction. Forexample, the number of modes may be 35 as used in HEVC, or some othernumber of modes greater than 35. Although the implementations may beapplied for intra prediction mode coding of only a few selected colorcomponents, such as a luma component or a chroma component, it would beapparent to one of ordinary skill in the art that they may be appliedfor all available color components (luma and both chroma), or in anyother combination.

According to some implementations of this disclosure, a video coder,such as video encoder 20 or video decoder 30, may check three or moreneighboring blocks of a group of neighboring blocks to identify intraprediction modes to generate a most probable modes (MPM) candidate listfor a current block. If a neighboring block is coded using an intraprediction mode, then the video coder may add the intra prediction modeused to code the neighboring block to the MPM candidate list for thecurrent block. The locations of the neighboring blocks checked by thevideo coder 20 may be fixed relative to the current block.

FIG. 5B is a block diagram illustrating exemplary locations of fivereconstructed neighboring blocks of a current coding block in accordancewith some implementations of the present disclosure. For example, thelocations of five neighboring blocks may include a left (L) block, anabove (A) block, a below left (BL) block, an above right (AR) block,and/or an above left (AL) block. Other locations of neighboring blocksmay also be used. The order in which intra prediction modes from theneighboring blocks are added to the MPM candidate list may depend onmany factors such as the current block size, whether the block is of acertain shape, such as rectangular or square, or based on contextinformation such as the size or shape of a neighboring block as well astype or frequency of intra prediction modes of the neighboring blocks.Note that five neighbor locations in FIG. 5B are provided as an example,but fewer or more neighboring blocks can be considered in theconstruction of the MPM candidate list using the implementations.

In general, a video coder can generate an MPM candidate list fromdifferent MPM types. The different types include, but are not limitedto, neighbor-based intra prediction modes, derived intra predictionmodes, and default intra prediction modes. A neighbor-based intraprediction mode refers to an intra prediction mode that is used for aneighboring block. A default intra prediction mode refers to a constantintra prediction mode that does not change with the neighboring blocks.The default intra prediction mode(s) may be one of a planar mode, a DCmode, a horizontal mode, or a vertical mode. A derived intra predictionmode refers to an intra prediction mode that is derived based on aneighbor-based intra prediction mode or a default intra prediction mode.A derived intra prediction mode may not be an actual intra predictionmode of a neighboring block. It may be an intra prediction mode that isderived from the actual intra prediction mode of the neighboring blockor derived in some other manner. For example, a derived intra predictionmode may be a neighbor-based intra prediction mode ±1, ±2, etc. Aderived intra prediction mode can also be generated by another existingderived intra prediction mode.

The video coder may add intra prediction modes to the MPM candidate listaccording to the intra prediction mode type. For example, the videocoder may first add neighbor-based intra prediction modes, then derivedintra prediction modes when the number of neighbor-based intraprediction modes is less than N, and then default intra prediction modeswhen the total number of neighbor-based intra prediction modes andderived intra prediction modes is still less than N. In anotherimplementation, the video coder may add intra prediction modes withdifferent types in an interleaved manner. For example, the video codermay add one or more default intra prediction modes after adding acertain number of neighbor-based intra prediction modes to the list.Alternatively, the video coder may add two neighbor-based intraprediction modes, two default intra prediction modes, and then moreneighbor-based intra prediction modes.

Only unique neighbor-based intra prediction modes are to be added to theMPM candidate list. For example, if one of the neighboring blocks hasthe same intra prediction mode, which has already been added to the MPMcandidate list, then such mode is not added to the list a second time.The location of a neighboring block may be represented by a sub-blocksize, for example 4×4, meaning that it is the granularity at which intraprediction mode information is stored. In another example, intraprediction mode information can be specified per pixel or for largerblocks, such as 8×8. If chroma is subsampled comparing to lumacomponent, such as in 4:2:0 color format, then the chroma componentsub-block location may be smaller, for example 2×2, which may correspondto luma 4×4.

In some implementations, depending on the neighboring block size,multiple locations of neighboring blocks depicted in FIG. 5B may belongto the same CU. For example, if a neighboring block is 16×16 and thecurrently coded block is 8x8, then the above left and left locations maybelong to the same 16×16 neighboring block, where the intra predictionmode information would be the same for those locations.

The number of neighbor locations M can be equal to the MPM candidatelist size N, but may be smaller or larger. In one example, the number Mmay be smaller than N to allocate some room to include other types ofintra prediction modes, e.g., derived or default intra prediction modes,into the MPM candidate list. The number of locations can depend on thecurrent and/or neighboring block's characteristics, such as block size,whether a block is square or rectangular, whether the rectangular blockis a horizontally-oriented rectangular block (width is greater thanheight) or a vertically-oriented rectangular block (width is smallerthan height), the ratio between height and width, and the ratio betweenthe larger and smaller value of height and width. The number oflocations may also depend on the neighboring block's prediction mode(e.g., intra or inter).

When a block is coded using an intra prediction mode, a video encoder(e.g., video encoder 20) may generate an MPM candidate list for theblock. A video decoder (e.g., video decoder 30) may generate the sameMPM candidate list as determined by the video encoder by implementingthe same MPM candidate list generation process implemented by the videoencoder. As the video encoder and video decoder generate the same MPMcandidate lists, the video encoder can signal an intra prediction modeto the video decoder by signaling an index value that corresponds to aparticular candidate in the MPM candidate list. Unless explicitly statedto the contrary, the MPM candidate list generation implementationsdescribed herein can be performed by either a video encoder or a videodecoder.

In addition to the aforementioned regular intra prediction modes,multiple MBIP modes have been proposed for performing the intraprediction to the current block from neighboring blocks by applyinglinear matrix transformation on the neighboring block reconstructedpixels. FIGS. 6A and 6B are block diagrams illustrating two matrix-basedintra prediction schemes of coding blocks of different sizes inaccordance with implementations of the present disclosure.

First, the reconstructed pixels from above and left neighboring blocksare filtered and optionally down-sampled. For example, for an 8×8 codingblock depicted in FIG. 6B, 8 pixels from above and left neighboringblocks, respectively, are down-sampled by factor of 2 to derive 4down-sampled pixels from each side. Likewise, for an 4×4 coding blockdepicted in FIG. 6A, 4 pixels from above and left neighboring blocks,respectively, are down-sampled by a factor of 2 to derive 2 down-sampledpixels from each side.

Second, the down-sampled pixels are rearranged into a one-dimensionalvector upon which the matrix multiplication with predefined matrices isperformed, followed with addition of a bias offset vector. After thematrix multiplication and bias offset, the results are re-arranged backto a two-dimensional array to form the matrix-transformedtwo-dimensional results. Depending on the current block size, the matrixtransformed two-dimensional results may be in a sub-sampled domain. Forexample, if the matrix transformed two-dimensional results have a sizeof 4×4, it is considered in a sub-sampled domain if the current blocksize is 8×8 (see, e.g., FIG. 6B) and it is considered not in asub-sampled domain if the current block size is 4×4 (see, e.g., FIG.6A).

Finally, for the scenario depicted in FIG. 6B, the matrix transformedtwo-dimensional results are up-sampled/interpolated to form a predictorfor the current coding block. But for the scenario depicted in FIG. 6A,the matrix transformed two-dimensional results already have a size of4×4, there is no need for up-sampling/interpolation to form a predictorfor the current coding block. It is worth noting that examples providedin FIGS. 6A and 6B are illustrative implementation.

Although MBIP overcomes some issues associated with the regular intraprediction mode, it nonetheless introduces some new challenges to thedesign and implementation of new codec standards. For example, 67 MBIPmodes require 67 matrices of coefficients and 67 bias offset vectors.Assuming that each matrix/vector coefficient is a 10-bit precisionnumber, it would take almost 8K bytes of memory space for storing thesevalues. This may increase the physical size and power usage of achip-based implementation of the MBIP.

In some implementations, instead of using 10-bit precision for eachcoefficient in the MBIP matrices and bias offset vectors, a lowerprecision is used to save the memory space required for storing thesecoefficients. For example, a 9-bit or even 8-bit precision is used foreach coefficient in the MBIP matrices and bias offset vectors to save atleast 10% of the memory space.

In some implementations, different precisions may be used forcoefficients in the MBIP matrices and bias offset vectors respectivelybecause the coding efficiency derived from MBIP is not as sensitive tothe precision of bias offset vectors as it is to the precision of theMBIP matrices. For example, 10-bit precision may still be used forcoefficients in the MBIP matrices and a lower precision (e.g., 9-bit orlower) is used for the coefficients in bias offset vectors. Further, itis possible to skip the bias offset vectors completely. In other words,MBIP only performs matrix multiplication on the pixels of theneighboring blocks and skips the addition of the bias vectors to savemore memory space if the quality of the reconstructed pixels issatisfactory.

In yet some implementations, only the MBIP matrices and bias vectorscorresponding to the smallest block size are stored in the memory whileother MBIP matrices and bias offset vectors corresponding to largerblock sizes are up-sampled and/or interpolated from those of thesmallest size. For example, only the matrices and bias offset vectorsdefined for a 4×4 block is saved. When the MBIP mode is applied to ablock of 8×8 or 16×16, the MBIP matrix and bias offset defined for the4×4 block is up-sampled and/or interpolated (e.g., bi-linearinterpolation) to the size defined for the 8×8 or 16×16 blockaccordingly and then used for predicting the current block.

As noted above in connection with FIGS. 6A and 6B, the filtering anddown-sampling operation is applied on the reconstructed pixels fromneighboring blocks, which requires extra logic and therefore physicalspace for codec implementation.

In some implementations, a 3-tap intra smooth filter, which is appliedon the reconstructed pixels of neighboring blocks in the regular intraprediction mode, is used in the filtering and/or down-sampling processunder the MBIP mode. In yet some implementations, no filtering operationis performed to the reconstructed pixels of neighboring blocks beforedown-sampling. In other words, down-sampling is performed on thereconstructed pixels from neighboring blocks directly without anyfiltering operation performed in advance.

The coding efficiency of intra mode is relied on not only the number ofangular coding modes but also the range of reconstructed samples thatcan be accessed. In some implementations, the reconstructed pixels fromtop right (AR), top left (AL) and bottom left (BL) blocks are also usedin the filtering and down-sampling process in the MBIP mode for bettercoding efficiency. Further, different numbers of reconstructed pixelsfrom the neighboring blocks may be used respectively from the topneighboring block (A) and from the left neighboring block (L) when acurrent block is coded using MBIP mode. For example, if the aspect ratioof a current block is non-square (e.g., a vertical rectangle), moreneighboring reconstructed pixels may be used from the left neighboringblock (L) along the longer side of the current block than the shorterside of the current block under MBIP mode. In some cases, only thereconstructed pixels from the neighboring block along the longer side ofthe current block are used under MBIP mode when the aspect ratio of acurrent block exceeds certain threshold (e.g., 3 to 1), and thereconstructed pixels from the neighboring block along the shorter sideof the current block are not used at all.

Matrix multiplication is a computationally expensive operation. Thereare certain situations in which the MBIP mode is disabled because thebenefit associated with MBIP is not justified when compared with thecomplexity associated with MBIP, e.g.,

-   -   If the width of the current block is four times larger than the        height of the current block;    -   If the height of the current coding block is four times larger        than the width of the current block;    -   If the width or height of current block is larger than 64; and    -   If the current block is a chroma block.

When this happens, a regular intra prediction mode may be used forpredicting a current block that meets one of the situations above and anMPM candidate list is generated for the current block accordingly asdescribed above. If one of the five neighboring blocks of the currentblock depicted in FIG. 5B is predicted using a MBIP mode, such MBIP modeneeds to be converted into a corresponding regular intra prediction modein order to be considered for predicting the current block.

FIG. 7 is a flowchart illustrating an exemplary process by which a videocoder implements the techniques of generating a most probable modes(MPM) candidate list in accordance with some implementations of thepresent disclosure. As described above, this video coder can be videoencoder 20 or video decoder 30. For illustrative purposes, thedisclosure below uses video encoder 20 as an example.

It is hereby assumed that video encoder 20 is to process a current blockof video data to be encoded. After determining that the current block isto be predicted using a regular intra prediction mode (e.g., one of the67 modes depicted in FIG. 5A), video encoder 20 needs to generate an MPMcandidate list for the current block by examining one or more of thefive neighboring blocks depicted in FIG. 5B. Video encoder 20 firstidentifies (710) a neighboring block located at a predefined locationrelative to the current block and its associated matrix-based intraprediction mode. Assuming that the left neighboring block L isidentified, video encoder 20 determines that the left neighboring blockL was reconstructed according to one of the MBIP modes. However, sincethe MBIP mode has been disabled for the current block, video encoder 20needs to determine what regular intra prediction mode is to beassociated with the left neighboring block L when generating the MPMcandidate list.

In some implementations, video encoder 20 determines (730) a regularintra prediction mode corresponding to the MBIP mode for the leftneighboring block L according to a predefined mathematical relationshipbetween the regular intra prediction modes and the matrix-based intraprediction modes. For example, video encoder 20 may assign a constantvalue (730-1) (e.g., planar mode 0) to the left neighboring block Lregardless of the actual MBIP mode used for predicting the leftneighboring block L. In other words, a constant value corresponding toone of the regular intra prediction modes is used for representing aneighboring block when video encoder 20 considers the neighboring blockfor updating the MPM candidate list of the current block.

In some implementations, the MBIP modes are designed such that there arespecific MBIP modes separately targeting block contents that favor DC,planar and/or directional intra prediction modes. For example, a MBIPmode (e.g., mode 0) is chosen to target block contents that favor planarprediction, a MBIP mode (e.g. mode 1) is chosen to target block contentsthat favor DC prediction; and a number of MBIP modes (with values largerthan 1) are chosen to target block contents that favor angularprediction with different directions. As a result, the mapping betweenMBIP modes and regular intra prediction modes becomes straightforward.

For example, assuming that MBIP intra prediction mode is defined asMode_(MBIP) and regular intra prediction modes as Mode_(INTRA) (whichranges from 0 to 66 according to VVC), when the total number of MBIPmode is also 67, there is a one-to-one mapping between regular intraprediction modes and MBIP modes as follows:

-   -   Mapping a regular intra prediction mode to a MBIP mode:        -   set Mode_(MBIP)=Mode_(INTRA)    -   Mapping a MBIP mode to a regular intra prediction mode:        -   set Mode_(INTRA)=Mode_(MBIP)

In other words, when a total number of the regular intra predictionmodes is the same as a total number of the matrix-based intra predictionmodes, the predefined mathematical relationship between the regularintra prediction modes and the matrix-based intra prediction modes isdefined as the regular intra prediction mode having a value being thesame as that of the matrix-based intra prediction mode (730-3).

When the total number of MBIP mode is 35, the following mapping logic isused for mode conversion:

-   -   Mapping a regular intra prediction mode to a MBIP mode:        -   if Mode_(INTRA) has a value smaller than 2, set            Mode_(MBIP)=Mode_(INTRA);        -   else, set Mode_(MBIP)=(Mode_(INTRA)−34)/2+18.    -   Mapping a MBIP mode to a regular intra prediction mode:        -   if Mode_(MBIP) has a value smaller than 2, set            Mode_(INTRA)=Mode_(MBIP);        -   else, set Mode_(INTRA)=(Mode_(MBIP)−18)×2+34.

Similarly, when the total number of MBIP mode is 19, the followingmapping logic is used for mode conversion.

-   -   Mapping a regular intra prediction mode to a MBIP mode:        -   if Mode_(INTRA) has a value smaller than 2, set            Mode_(MBIP)=Mode_(INTRA);        -   else, set Mode_(MBIP)=(Mode_(INTRA)−34)/4+10.    -   Mapping a MBIP mode to a regular intra prediction mode:        -   if Mode_(MBIP) has a value smaller than 2, set            Mode_(INTRA)=Mode_(MBIP);        -   else, set Mode_(INTRA)=(Mode_(MBIP)−10)×4+34.

When the total number of MBIP mode is 11, the following mapping logic isused for mode conversion:

-   -   Mapping a regular intra prediction mode to a MBIP mode:        -   if Mode_(INTRA) has a value smaller than 2, set            Mode_(MBIP)=Mode_(INTRA);        -   else, set Mode_(MBIP)=(Mode_(INTRA)−34)/8+6.    -   Mapping a MBIP mode to a regular intra prediction mode:        -   if Mode_(MBIP) has a value smaller than 2, set            Mode_(INTRA)=Mode_(MBIP);        -   else, set Mode_(INTRA)=(Mode_(MBIP)−6)×8+34.

In other words, when a total number of the regular intra predictionmodes is greater than a total number of the matrix-based intraprediction modes, the predefined mathematical relationship between theregular intra prediction modes and the matrix-based intra predictionmodes is defined as two categories: (i) non-angular intra predictionmode (less than mode 2) and (ii) angular intra prediction mode (equal orgreat than mode 2) (730-5). But it is noted that, in all these cases,there is no need for storing any mapping table for MPM list generationwhen MBIP mode is enabled together with regular intra prediction mode.

After determining a regular intra prediction mode, video encoder 20inserts (750) the regular intra prediction mode associated with theneighboring block into the most probable modes candidate list accordingto a predefined order as described above in connection with FIG. 5B.

In some implementations, position-dependent intra prediction combination(PDPC) is applied on the predicted samples formed through regular intraprediction to improve the intra prediction coding efficiency. The codinggain of PDPC comes from predictor quality improvement resulted from thecombination of intra predicted sample and the reconstructed pixels fromneighboring blocks. PDPC can be performed on top of the MBIP mode. Inother words, PDPC operation is performed on the predictor of a currentblock formed through MBIP. Certainly, such operation increases thecomputational complexity of encoding/decoding operations and should beused at selective locations where the benefit outweighs the cost.

In one or more examples, the functions described may be implemented inhardware, software, firmware, or any combination thereof. If implementedin software, the functions may be stored on or transmitted over, as oneor more instructions or code, a computer-readable medium and executed bya hardware-based processing unit. Computer-readable media may includecomputer-readable storage media, which corresponds to a tangible mediumsuch as data storage media, or communication media including any mediumthat facilitates transfer of a computer program from one place toanother, e.g., according to a communication protocol. In this manner,computer-readable media generally may correspond to (1) tangiblecomputer-readable storage media which is non-transitory or (2) acommunication medium such as a signal or carrier wave. Data storagemedia may be any available media that can be accessed by one or morecomputers or one or more processors to retrieve instructions, codeand/or data structures for implementation of the implementationsdescribed in the present application. A computer program product mayinclude a computer-readable medium.

The terminology used in the description of the implementations herein isfor the purpose of describing particular implementations only and is notintended to limit the scope of claims. As used in the description of theimplementations and the appended claims, the singular forms “a,” “an,”and “the” are intended to include the plural forms as well, unless thecontext clearly indicates otherwise. It will also be understood that theterm “and/or” as used herein refers to and encompasses any and allpossible combinations of one or more of the associated listed items. Itwill be further understood that the terms “comprises” and/or“comprising,” when used in this specification, specify the presence ofstated features, elements, and/or components, but do not preclude thepresence or addition of one or more other features, elements,components, and/or groups thereof.

It will also be understood that, although the terms first, second, etc.may be used herein to describe various elements, these elements shouldnot be limited by these terms. These terms are only used to distinguishone element from another. For example, a first electrode could be termeda second electrode, and, similarly, a second electrode could be termed afirst electrode, without departing from the scope of theimplementations. The first electrode and the second electrode are bothelectrodes, but they are not the same electrode.

The description of the present application has been presented forpurposes of illustration and description, and is not intended to beexhaustive or limited to the invention in the form disclosed. Manymodifications, variations, and alternative implementations will beapparent to those of ordinary skill in the art having the benefit of theteachings presented in the foregoing descriptions and the associateddrawings. The embodiment was chosen and described in order to bestexplain the principles of the invention, the practical application, andto enable others skilled in the art to understand the invention forvarious implementations and to best utilize the underlying principlesand various implementations with various modifications as are suited tothe particular use contemplated. Therefore, it is to be understood thatthe scope of claims is not to be limited to the specific examples of theimplementations disclosed and that modifications and otherimplementations are intended to be included within the scope of theappended claims.

1. A method for video coding, comprising: identifying a neighboringblock located at a predefined location relative to a current block andits associated matrix-based intra prediction mode; determining a regularintra prediction mode corresponding to the matrix-based intra predictionmode for the neighboring block according to a predefined mathematicalrelationship between multiple regular intra prediction modes andrespective matrix-based intra prediction modes; and inserting theregular intra prediction mode associated with the neighboring block intoa mode candidate list according to a predefined order.
 2. The method ofclaim 1, wherein the predefined mathematical relationship is defined asthe multiple regular intra prediction modes being a constant value forthe respective matrix-based intra prediction modes.
 3. The method ofclaim 2, wherein the constant value is equal to 0 and corresponds to aplanar mode.
 4. The method of claim 1, wherein identifying theneighboring block comprises: identifying a plurality of neighboringblocks including the neighboring block.
 5. The method of claim 4,wherein the number of the plurality of neighboring blocks is smallerthan a size of the mode candidate list.
 6. The method of claim 4,wherein the plurality of neighboring blocks comprise a left block and anabove block.
 7. The method of claim 1, wherein each matrix-based intraprediction mode has an associated matrix and a bias vector.
 8. Themethod of claim 1, further comprising: obtaining an index valuecorresponding to a particular candidate in the mode candidate list. 9.An electronic apparatus comprising: one or more processing units; amemory coupled to the one or more processing units; and a plurality ofprograms stored in the memory that, when executed by the one or moreprocessing units, cause the electronic apparatus to perform actscomprising: identifying a neighboring block located at a predefinedlocation relative to a current block and its associated matrix-basedintra prediction mode; determining a regular intra prediction modecorresponding to the matrix-based intra prediction mode for theneighboring block according to a predefined mathematical relationshipbetween multiple regular intra prediction modes and respectivematrix-based intra prediction modes; and inserting the regular intraprediction mode associated with the neighboring block into a modecandidate list according to a predefined order.
 10. The electronicapparatus of claim 9, wherein the predefined mathematical relationshipis defined as the multiple regular intra prediction modes being aconstant value for the respective matrix-based intra prediction modes.11. The electronic apparatus of claim 10, wherein the constant value isequal to 0 and corresponds to a planar mode.
 12. The electronicapparatus of claim 9, wherein identifying the neighboring blockcomprises: identifying a plurality of neighboring blocks including theneighboring block.
 13. The electronic apparatus of claim 12, wherein thenumber of the plurality of neighboring blocks is smaller than a size ofthe mode candidate list.
 14. The electronic apparatus of claim 12,wherein the plurality of neighboring blocks comprise a left block and anabove block.
 15. The electronic apparatus of claim 9, wherein eachmatrix-based intra prediction mode has an associated matrix and a biasvector.
 16. The electronic apparatus of claim 9, wherein the actsfurther comprise: obtaining an index value corresponding to a particularcandidate in the mode candidate list.
 17. A non-transitory computerreadable storage medium storing a plurality of programs for execution byan electronic apparatus having one or more processing units, wherein theplurality of programs, when executed by the one or more processingunits, cause the electronic apparatus to perform acts comprising:identifying a neighboring block located at a predefined locationrelative to a current block and its associated matrix-based intraprediction mode; determining a regular intra prediction modecorresponding to the matrix-based intra prediction mode for theneighboring block according to a predefined mathematical relationshipbetween multiple regular intra prediction modes and respectivematrix-based intra prediction modes; and inserting the regular intraprediction mode associated with the neighboring block into a modecandidate list according to a predefined order.
 18. The non-transitorycomputer readable storage medium of claim 17, wherein the predefinedmathematical relationship is defined as the multiple regular intraprediction modes being a constant value for the respective matrix-basedintra prediction modes.
 19. The non-transitory computer readable storagemedium of claim 18, wherein the constant value is equal to 0 andcorresponds to a planar mode.
 20. The non-transitory computer readablestorage medium of claim 17, wherein identifying the neighboring blockcomprises: identifying a plurality of neighboring blocks including theneighboring block.